We're going to look now at an animal whose habitat is slowly disappearing. Polar bears live on sea ice. But Arctic sea ice, which used to stay frozen in the summertime, is now slowly disintegrating. This poses a unique challenge for scientists, government officials and others. How do you preserve the polar bear and prevent it from going extinct decades from now? Juliet Eilperin of The Washington Post has been reporting on this issue. And she joins us now to talk about what she's learned.

Juliet, good morning.

JULIET EILPERIN: Morning.

GREENE: So how urgent is this problem, really?

EILPERIN: Well, one of the things that's interesting about it is that while it's urgent in the sense that the consequences are dire, we are talking about some years from now. Scientists project that summer sea ice could disappear completely by 2030 or even a little before then.

And to some extent some of this warming is already locked in. So while we could cut greenhouse gas emissions to slow the deterioration of the sea ice, there's no question the sea ice is melting and as a result we could very likely see polar bear populations plummet in the years ahead.

GREENE: You have talked in your reporting to a number of zoos who are pushing to bring in a handful of polar bears into captivity I understand in part to preserve the gene pool. So tell us exactly who this would work.

EILPERIN: So what's happening right now is that while there are a number of polar bears that are out there - their estimates vary between 20,000 and 25,000 worldwide - that's where things stand right now - there's a concern that if their numbers dwindle, particularly in certain areas since there are basically 19 groupings of polar bears in the Arctic, that you could see a narrowing of the gene pool. And as a result often, you know, when there's a lack of genetic diversity sometimes animals are less resilient when faced with other pressures. And so the idea would be that while there are a certainly polar bears in American zoos, as well as zoos throughout the world, basically you would have some in captivity so that we would work on learning how to breed them, which is something that's not done right now in terms of artificial insemination.

GREENE: And what are the obstacles, you know, preventing this? I mean this sounds like a good idea in theory.

EILPERIN: Well, right now there's a pretty formidable legal obstacle. Right now, under current U.S. law, you can't import bears for the purpose of public display. You can import them for scientific research if you can argue that it will directly lead to the recovery of the species. But the Fish and Wildlife Service has told zoo officials that this does not meet the threshold of the legal requirements. And so essentially, they're examining whether under a future recovery plan this purpose could qualify as an exemption under the Marine Mammal Protection Act.

GREENE: Juliet, stay with us, if you don't mind, for a moment because I want to bring in another voice. The St. Louis Zoo is preparing to build a $20 million polar bear exhibit over the next five years. And Jeffrey Bonner is the president and CEO. And he joins us also on the line from member station KWMU in St. Louis. Good morning.

DR. JEFFREY BONNER: Good morning, David.

GREENE: So tell us if you can, Dr. Bonner, your zoo, as I understand, once had some polar bears, about a dozen of them. What happened to them?

BONNER: Well, we've had polar bears since the 1920s. I think we've had about 15 bears over that span of time. Our last bear died of liver cancer and, you know, we really needed to do the new exhibit, you know, state of the art in 1920, it's not today. Now the new one will be huge. I have wonderful swimming in a very large exhibit with natural substrates so they can dig and do the things that polar bears do when they're on land.

Bears are marine mammals. They make a living off the sea ice. But bears have come on land, particularly around Churchill and Manitoba, which is a great place to see polar bears in a huge concentration.

GREENE: And when you say Churchill, we're talking about parts of Canada?

BONNER: Yeah. So they have what we call sort of a walking hibernation during the summers where it's quite warm, and then the ice forms an then they go back on the ice.

GREENE: What's happening now is that the ice is forming much later in the year and disappearing much earlier in the year so that walking hibernation lasts longer, and that's why you're getting a lot of stranded bears, nuisance bears and why you're seeing so many problems in Churchill. And that's where the manifestation of global warming is going to hit first and hit hardest.

Can they live on land year-round in theory if there's no ice left one day?

BONNER: No they can't live on land. They do try and eat eggs but that number of bears would wipe out the nest and the eggs of the sea birds in no time at all. They simply can't survive on land. It's an impossibility.

GREENE: Juliet Eilperin, let me turn back to you. You know, this is not a first. I mean zoos have successfully helped preserved species that were in danger before. Give us a few examples of that.

EILPERIN: Zoos have been very important in conserving imperiled species, such as the California condor, the Mexican wolf and even the American bison. But one of the really hard questions about polar bears is if we take them into captivity and through climate change the sea ice disappears what are we saving them for if ultimately we destroy their habitat and they can't return to the wild?

GREENE: There might just be no place to reintroduce them.

EILPERIN: Exactly.

GREENE: All right. It's been interesting talking about this with both of you.

Juliet Eilperin is a reporter with The Washington Post. Thanks so much for being here, Julia.

EILPERIN: Thank you.

GREENE: And Jeffrey Bonner is president and CEO of the St. Louis Zoo. Thank you for being here.